1. Field of the Invention
The invention relates generally to cartridge-type water filters and more specifically to centrifugal cleaning such cartridge filter elements by spinning them on an axle with a water jet.
2. Description of the Prior Art
The typical swimming pool recirculation pump is a centrifugal pump which moves the water by centrifugal force. Water is drawn into the eye of the impeller and then thrown from the outer perimeter of the whirling impeller into the chamber enclosing the impeller and then forced into the piping system. If the water has been filtered prior to reaching the pump, at the suction side of the pump, it is discharged from the pump directly back to the pool. The filter system may be either a vacuum or gravity system. If the water has not been filtered, it is discharged from the pump to a filter station and then on to the pool. This is a so-called pressure system since the water is delivered to the filters under pressure.
Filtration is the physical process of removing dirt particles and solids to prevent impeding the disinfecting process and to promote clarity. Filtration, capable of removing some bacteria, is not a disinfecting process. Disinfecting is the chemical process of killing disease-causing bacteria and other types of microorganisms by maintaining a uniformly dispersed residual of some chemical, usually chlorine, in pool waters. The removal of bacteria by filtration is not considered particularly beneficial. The primary purpose of filtration is to remove all foreign particles which would otherwise increase the disinfectant demand of the water, thus lowering chlorine residuals and weakening the killing power of the chemicals that have been added to sterilize the water. Many alternatives are open to designers and builders to accomplish particle removal through filtration.
As the soil removal process takes place in the filter, the dirt accumulation increases resistance to flow and eventually reduces the flow below the specified amount. At that point the filter must be cleaned. Unicel (Burbank, Calif.) recommends cleaning the filter when the pump output pressure rises 8-10 PSI above the initial or new cartridge starting pressure. Conversely, when the filter is cleaned and returned to service, resistance to flow is at its minimum and flow is at its maximum. Thus, it can be seen that the swimming pool pump output varies over the filter life of the cartridge.
There are five basic filter types traditionally used, e.g., pressure sand, pressure diatomaceous earth, vacuum diatomaceous earth, gravity sand, and cartridge.
Cartridge filter manufacturers typically recommend cleaning the cartridge by first removing it from the filter housing, and rinsing it with a garden hose to remove loose debris. For example, the Modular D.E. Filter marketed by STA-RITE Pool/Spa Group (Waterford, Wis.) must have the tank that contains it opened so the filter can be rinsed. The use of commercial cartridge cleaners are also suggested in other cases, e.g., Guardex Filter Cleaner. The typical filter cartridge is soaked in a separate solution of one part Muriatic acid to twenty parts water until the bubbling stops to remove calcium or mineral buildup. The element is thoroughly rinsed before putting it back in the filter housing. All oils and cleaning solution must be removed from the cartridge before soaking it in the acid solution, otherwise the acid reactions with the residue will permanently clog the filter material.
A typical cartridge filter takes about twenty minutes to clean with a garden hose because each of the longitudinal pleat folds must be combed with water. The force of the water is also pushing the filter cake deeper into the filter medium since the dirt buildup typically occurs on the outside diameter.
Taking cartridge filters out and cleaning them periodically is a chore many pool-owners skip. So to make such chore easier, it has become popular to install as many as four large cartridge filters. The over-capacity is so great, that the filters need only be taken out and cleaned once a season. But this has not really solved the problem because the filter costs are quadrupled and experience is showing these filters too are not being cleaned every season. A cartridge filter that sits dirty too long becomes impacted and cannot come clean, and so a new one must be purchased.
Most filter cartridges are supported inside with a perforated tube. Such tube prevents spin-cleaning from the inside with a water jet because the perforations are too small and few. So these can only be spin-cleaned by directing cleaning-water jets from outside inward toward the filter.
In normal operation, most filter cartridges receive the dirty water to-be-filtered on their submerged outside surfaces. The filtered water is collected inside the volume of the filter cartridge and drains out to the pool. So cleaning involves spinning the cartridge to generate centrifugal force to fling off filter cake and debris, and directing a water jet from inside or outside.